It is necessary in mechanisms which require accuracy of operation, such as lathes, milling machines, indexing machines and numerous other machine tools, to provide some sort of anti-backlash mechanism in the gear train, so that repeatable positioning or indexing of the cutting tool is obtainable. Prior art methods typically use split gears with some sort of spring device to bias the gears in opposite rotational directions about a common shaft. One problem with such spring-loaded split gear configurations, is that the spring force must be overcome when installing the gear assembly i.e., engaging mating gears. This may be difficult to accomplish if the spring loads are large.
A more sophisticated approach can be found in U.S. Pat. No. 4,072,064 "Anti-Backlash Gear Assembly" by W. D. Lloyd. Here, the anti-backlash gear assembly includes a hydraulic cylinder that automatically maintains clearance filling positioning of two circumferentially and axially adjustable segments of a split gear. However, this device is complicated and expensive when compared to simple spring biasing systems. Furthermore, the cylinder may leak which could cause a loss of the anti-backlash feature.
Another approach can be found in U.S. Pat. No. 3,803,936 "Adjustable Herringbone Gears for use in Embossing, Engraving, and the Like" by B. Kroeper. This invention relates to a set of herringbone gears for use in a rotary embossing and engraving apparatus. One of the gears has three segments with an adjustable center segment in order to obtain positive contact between the teeth on the adjustable center segment and the teeth of the mating gear to prevent backlash and longitudinal side trust on the gears. A cam shaft is mounted in a hole extending through the center and side gear segments having a cam lobe located in the center segment. Rotation of the cam shaft causes the cam lobe to engage and position the center segment. With this system, once the prepositioning is accomplished by the cam, no variation is possible. Thus, if this type of anti-backlash gear assembly were mated with a rack gear which varied in distance from the center line of the gear assembly, slack or binding would appear as the gear traversed the rack gear causing a loss of the anti-backlash feature. Other patents of interest are U.S. Pat. No. 2,880,625 "Backlash Compensator" by A. G. Thomas, U.S. Pat. No. 4,582,360 "Hinge for Seat with Adjustable Backrest, Particularly Power Vehicle Seat" by P. Becker, U.S. Pat. No. 2,703,497 "Biasing Mounting" by V. G. Townsend, U.S. Pat. No. 2,679,167 "Antibacklash Device" by D. B. Nichinson, U.S. Pat. No. 4,305,307 "Anti-Backlash Gear Drive" by P. C. Kiunke, and U.S. Pat. No. 2,382,846 "Differential Gearing" by C. C. Barber.
Thus, while there are numerous anti-backlash gear assemblies available, none provide the combination of simple spring biasing means for relieving the biasing force for installing the anti-backlash gear assembly, means for automatically adjusting the amount of anti-backlash force on while in operation in one simple, reliable and inexpensive assembly.
Therefore, it is a primary object of the subject invention to provide an anti-backlash gear assembly of the split-gear type wherein the gears are spring biased apart.
It is another object of the subject invention to provide an anti-backlash gear assembly wherein the gear assembly is easily mated with other gears without the need for overcoming the anti-backlash biasing force.
It is a further obJect of the subject invention to provide an anti-backlash gear assembly wherein the amount of biasing force can be varied.
It is a still further object of the subject invention to provide an anti-backlash gear assembly wherein automatic dynamic adjustment is provided to compensate for tolerance build up and wear.